This invention relates to austenitic manganese steel. This steel is also known as Hadfield Manganese Steel, named for the inventor Robert Hadfield, British Pat. No. 200 of 1883. In this patent, the upper limit for manganese was set at 20%; in subsequent studies published in 1886, the upper limit was extended to 21%. Hadfield also discovered the toughening process ("austenitizing") by which the properties of the steel, as cast, could be improved, producing exceptional toughness and work-hardening properties, by heating the casting up to 1050.degree. before quenching: British Pat. Nos. 11833 of 1896 and 5604 of 1902. As to the foregoing, see the Introduction in MANGANESE STEEL published 1956 by Oliver and Boyd, Edinburgh and London.
The author of "Austenitic Manganese Steel" (METALS HANDBOOKS, 8th Edition, 1961) states acceptable properties for this steel may be produced up to at least 20%. We are colleagues of the author, and have been for a number of years, and know that in actual practice over a period of many years he perceived and suggested no advantage in exceeding about 14% manganese, 1.2% carbon. The standard alloy, indeed, is and has been about 12% manganese, 1% carbon for a long time. A rule of thumb in the art is that the nominal or desirable carbon limit is about one-tenth the manganese content in percent by weight.
One major advantage of the steel is its ability to withstand wear because of its inherent work-hardening character. For this reason castings subjected to constant abuse such as liners and mantles for gyratory crushers, railroad crossings, teeth for dipper and dredge buckets, wear plates and the like have been composed of this steel.
We are also aware of U.S. Pat. Nos. 4,130,418 and 4,394,168 which address Hadfield steels of high manganese, high carbon content, which will be discussed below.